Incubators for clinical analyzers require test elements, particularly slide-like test elements, to be inserted, incubated, and then removed for analysis. The most common incubator has stations disposed around a rotor such that the same opening into the rotor functions both as an inlet port and an outlet port.
Slide elements conventionally come with one datum or reference surface that is used to ensure the proper location of the element in the analyzer. This datum surface is usually the trailing edge as the element comes off its storage site, which usually is a cartridge. By such means, the pusher blade used to remove the element from its storage can also be used to properly locate the element via its trailing edge at the sample dispensing station. If the element goes immediately from the dispensing station to an incubator, the datum surface is the outer, trailing edge of the element in the rotor. However, in analyzers such as those available from Eastman Kodak Co. under the trademark "Ektachem 700" analyzers, the element is inserted first into an intermediate station, e.g., the slide distributor in the "Ektachem 700" analyzer. When it comes off the intermediate station into the incubator rotor, the datum surface has been reversed and goes in first into the rotor so as to be the inside edge or surface, not the outer edge or surface. The inside datum surface in such analyzers is pushed up against a fixed surface to properly locate it for an incubator reading by a reflectometer. (The surface or edge of the element opposite to the datum surface is not useful, since the length of the slide element can vary.)
Although such fixed incubator surfaces work, they have a disadvantage: It is difficult to control the location of such fixed rotor surfaces, particularly since the rotor may deviate as it rotates about its axis, from being on true center. Such deviations of the rotor during rotation are called "out-of-round" deviations, created by rotor surfaces that are not perfectly concentric with the rotor's center of rotation.
Therefore, there has been a need prior to this invention to control an inside-positioned datum surface of a slide element by means other than a fixed stop.